Two-stage refrigeration system having crankcase pressure regulation in high stage compressor

ABSTRACT

A two-stage refrigeration system including a condensor, a receiver, an evaporator, a low-stage dry-wall compressor and a high-stage dry-wall compressor, the low-stage compressor including an oil-draining assembly for automatically draining oil from the suction chamber to the crankcase chamber, and a pressure-equalizing connection between the suction chamber and the crankcase chamber, the high-stage compressor having an oildraining assembly for automatically draining oil from the highstage suction chamber to the high-stage crankcase chamber, and a pressure connection between the high-stage crankcase chamber and the low-stage crankcase chamber; and a pressure-responsive regulating valve interposed in the connection between the highstage crankcase chamber and the low-stage crankcase chamber, the pressure-responsive valve being connected to respond to the highstage suction chamber pressure to maintain a predetermined pressure differential of one pound per square inch between the high-stage suction chamber and the high-stage crankcase chamber.

United States Patent 1 Grant 1 March 6, 1973 E} (5]. ..62/l93, szl v rgeg fig nection between the high-stage crankcase chamber n n e e c c e ce c c c c c c e e e e e c e I e e e c c e a [58] Flew of Search"184/616; 62/192 responsive regulating valve interposed in the connec-62/420 510 tion between the high-stage crankcase chamber and thelow-stage crankcase chamber, the pressure- [56] References C'tedresponsive valve being connected to respond to the UNITED STATES PATENTShigh-stage suction chamber pressure to maintain a predetermined pressuredifferential of one pound per 3,2223% g ril square inch between thehigh-stage suction chamber e 1e 3,494,137 2/1970 Cargo ....62/420 andthe stage crankcase chamber 3,500,962 3/1970 Kocher ..62/ 193 9 Claims 2Drawing Figures Primary Examiner-Meyer Perlin Attorney-James E. Nilleset al.

EVA PO R A T o R co N D EN 5 E R RE c El v E R TWO-STAGE REFRIGERATIONSYSTEM HAVING CRANKCASE PRESSURE REGULATION IN HIGH STAGE COMPRESSORInventor: Whitney 1. Grant, Muskego, Wis.

Assignee: Vilter Manufacturing Corporation,

Milwaukee, Wis.

Filed: Oct. 8, 1971 Appl. No.: 187,800

[57] ABSTRACT A two-stage refrigeration system including a condensor, areceiver, an evaporator, a low-stage dry-wall compressor and ahigh-stage dry-wall compressor, the low-stage compressor including anoil-draining assembly for automatically draining oil from the suctionchamber to the crankcase chamber, and a pressureequalizing connectionbetween the suction chamber and the crankcase chamber, the high-stagecompressor having an oil-draining assembly for automatically drainingoil from the high-stage suction chamber to the high-stage crankcasechamber, and a pressure con- INTER COOLER PATENTEDMAR' 5 I973 FIGJ EVAPO RATO R CONDENSER RECEIVER COOLER INTER- INVENTOR -B/IN? ATTORNEYTWO-STAGE REFRIGERATION SYSTEM HAVING CRANKCASE PRESSURE REGULATION INHIGH STAGE COMPRESSOR BACKGROUND OF THE INVENTION In most two-stagerefrigeration systems, the presence of oil vapor in the suction chambersis not considered detrimental to the operation of the system. Where highaccumulations are anticipated, automatic draining systems have beenprovided such as shown in US. Pat. No. 3,543,800. In this type of asystem, the pressure in the crankcase chamber has been maintained equalto the pressure in the second stage suction chamber to reduce operatingforces on the compressor bearings and rod seals so that they do notbecome overloaded. However, it has now been determined that the oilwhich is miscible in halocarbon refrigerants is often carried alongthrough the refrigeration system with the gaseous refrigerant andcollects in the various parts of SUMMARY OF THE INVENTION The two-stagerefrigeration system of the present invention contemplates the use ofdrywall compressors and reduces the possibility of oil vapors beingcarried into the compressor suction and discharge chambers to a minimum.In my copending application, Ser. No. 187,801, entitled Single Stage DryCylinder Compressor Having Automatic Oil Drain from Suction Chamber toCrankcase, an automatic oil draining assembly has been disclosed'for asingle-stage drywall compressor. However, in a two-stage drywallcompressor system, the use of such an assembly on each stage has notbeen adequate to provide the necessary reduction of oil vapor in thesystem. In the present system, the pressure in the high-stage suctionchamber and high-stage crankcase chamber is maintained at apredetermined pressure differential to eliminate overloading of thecompressor bearings and piston rod and to assure that gas pressureleakage is from the high-stage suction chamber into the high-stagecrankcase chamber.

Other advantages of the present invention become apparent from thefollowing detailed description when read in connection with theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of thetwo-stage drywall compressor refrigeration system of the presentinvention; and

FIG. 2 is an electrical diagram of the circuit arrangement for the oilreturn assemblies.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A refrigeration system ascontemplated herein is shown in FIG. 1 of the drawings and as seentherein, the refrigeration system includes a low-stage compressor 10, ahigh-stage compressor 12, a condenser 14, a receiver 16, and anevaporator 18. As is generally understood in the art, the low-stagecompressor 10 is connected to the high-stage compressor 12 by means of adischarge conduit 20. The high-stage compressor 12 is serially connectedto the low-stage compressor 10 through the condenser 14, receiver 16 andevaporator 18 by means of high-pressure discharge conduit 22, liquidrefrigerant conduit 24, high-pressure refrigerant conduit 26 and suctionpressure conduit 28. A refrigerator control valve 25 is provided inconduit 28 to reduce pressure at the entrance of the evaporator.Low-Stage Compressor The low-stage compressor 10 includes a low-stagedischarge chamber 30, a low-stage suction chamber 32, and a low-stagecrankcase chamber 34. Means are provided to equalize the pressurebetween the suction chamber 32 and crankcase chamber 34 in the form ofan equalizing line 36. Oil vapor is prevented from entering the suctionchamber through the equalizing line 36 by means of an oil filteringdevice 38.

Means are provided to automatically drain oil from the suction chamber32 back to the crankcase chamber 34, as more fully discussed in mycopending application Ser. 187,801. Such means is in the form of anautomatic oil return assembly 40 which includes a reservoir 42Loperatively connected to allow oil to flow from the suction chamber 32to the reservoir 42L by oil conduits 44 and operatively connected toallow oil to flow from the reservoir 42L to the crankcase chamber 34 byoil conduit 46. One-way check valves 48L and 50L are provided,respectively, in the oil conduits 44L and 46L to prevent reverse flow ofoil through either of the conduits 44 or 46.

The flow of oil from the suction chamber to the reservoir 4.2 iscontrolled by means of a solenoid valve 52L interposed in a pressureline 54 provided between the suction chamber and the reservoir 42. Thesolenoid valve is normally open to equalize pressure between the suctionchamber 32 and the reservoir 42L to allow any oil which accumulates inthe suction chamber 32 to flow freely through the oil conduits 44 to thereservoir 42L.

Oil is forced from the reservoir 42L through the conduit 46L and intothe crankcase chamber 34 by connecting the reservoir 42 to the dischargeconduit 20 by conduit 56 to allow the high-pressure dischargerefrigerant to enter the reservoir 42L. The flow of highpressure'refrigerant is controlled by means of a second solenoid valve 58Linterposed in the conduit 56, which is normally closed when solenoidvalve 52L is open. When solenoid valve SSL is opened, solenoid valve 52Lis closed and the pressure in conduit 56 and reservoir 42 rises to forcethe oil through the oil conduit 46 into the crankcase chamber. The rateof pressure rise in the reservoir 42 can be restricted by means of arestricted orifice 60 provided in conduit 56.

Means are provided to selectively control the solenoids 52L and SSL inresponse to the level of oil in the reservoir 42L. Such means is in theform of a float valve 62L provided in the reservoir and operativelyconnected through a circuit as shown in FIG. 2 to the solenoids 52 and58 to close the solenoid 52 and open the solenoid 58 whenever the oil inthe reservoir reaches a predetermined height. The operation of theelectrical circuit in FIG. 2 isdescribed below.

High-Stage Compressor The high-stage compressor 12 includes ahigh-stagedischarge chamber 64, a high-stage suction chamber 66 and acrankcase chamber 68. Means are provided to allow for the flow of oilfrom the suction chamber 66 to the high-stage crankcase chamber 68 inthe form of an oil-return assembly 70. The assembly 70 operates insubstantially the same manner as oil-return assembly 40.

The flow of oil from the suction chamber 66 to the reservoir 421-! iscontrolled by means of a solenoid valve 52H interposed in a pressureline 54H provided between the suction chamber 66 and the reservoir 42H.The solenoid valve 52H is normally open to equalize pressure betweensuction chamber 66 and the reservoir 42H to allow any oil whichaccumulates in the suction chamber 66 to flow freely through the oilconduits 44H to the reservoir 42H.

Oil is forced from the reservoir 42H through the conduit 46H into thecrankcase chamber 68 by connecting the reservoir 421-] to the dischargeconduit 20 by a gas pressure conduit 56H to allow the high-pressuredischarge refrigerant to enter the reservoir 421-1. The flow ofhigh-pressure refrigerant is controlled by means of a second solenoidvalve 58H interposed in the conduit 561-! which is normally closed whensolenoid valve 521-! is open. When solenoid valve 58H is opened,solenoid valve 52H is closed and the pressure of the gaseous refrigerantin the conduit 56B is applied to the reservoir 42H to force the oil intothe crankcase chamber 68. The rate of pressure rise in the reservoir 42His restricted by means of an orifice 60 provided in conduit 56H.

Means are provided to selectively control the solenoids 52H and 581-! inresponse to the level of oil in the reservoir 42H. Such means is in theform of a float 1 valve 62H provided in the reservoir 42H andoperatively connected through the circuit shown in FIG. 2 to thesolenoids 52H and 58H. Whenever the oil in the reservoir42l-l reachestapredetermined level, the float valve will deenergize solenoid 521-! toclose conduit 54H and will open solenoid 58H and connect the reservoir42H to the high-pressure discharge chamber 64. Control Circuit Thecontrol circuit for the two oil drain assemblies and 70 are identical asseen in FIG. 2. The description of the circuit for controlling solenoids52L and 58L is therefore described below. However, it should beunderstood that the description for the circuit for solenoids 52H and581-! is the same. As seen in FIG. 2, the float control valve 62L isconnected across lines L,-L, in series with timer 80 by lines 82. Thesolenoids 521. and 58L are alternately connected across the lines L L,by timer switch 84 connected to line 86. A holding circuit is set upbetween the timer 80 and the solenoid 58L by a bypass line 88.

In operation, the solenoid valve 52L is normally energized by closedswitch 84. When the float valve 62L closes to energize timer 80, switch84 will open the circuit through solenoid 52L and close the circuitthrough solenoid 58L. The timer 80 will run for a preset time intervalto allow for the complete discharge of oil from the reservoir 42L sincethe float valve 62L will open as soon as oil starts to drain fromreservoir 42L. When the timer 80 opens the timer switch 84, thesolenoids 58L and timer 80 will be deenergized and solenoid 52L will beenergized.

Pressure-Regulating Valve Assembly In accordance with the invention, thepressure differential between the high-pressure suction chamber 66 andthe high-pressure crankcase chamber 68 is controlled by means of apilot-operated pressure-regulating valve 72. In this regard, thecrankcase chamber 68 is connected to the low-pressure crankcase chamber34 by means of-a gas pressure conduit 74. The low-pressure dischargechamber 30 is connected to the highpressure suction chamber 66 by meansof the gas pressure conduit 20. An intercooler 76 may be provided in thedischarge pressure conduit 20, if desired.

The pilot-operated pressure-regulating valve is interposed in the gaspressure conduit 74 and is operatively connected to the dischargepressure conduit 20 by means of a bypass conduit 78. The pilot-operatedpressure-regulating valve 72 is set to maintain the pressure in thehigh-pressure crankcase chamber 68 approximately 1 pound per square inchbelow the pressure of the high-pressure suction chamber 66. Bymaintaining this pressure differential at 1 pound per square inch, anyoil vapor present in the high-pressure crankcase chamber 68 will beprevented from flowing into the high-pressure suction chamber 66. Sincea one-pound pressure differential always exists between the highstagesuction chamber 66 and the high-stage crankcase chamber 68, a continualinternal leakage of gas will occur between the suction chamber 66 andcrankcase chamber 68.

In operation and under stable operating conditions, thepressure-regulating valve 72 will constantly bleed crankcase chamberpressure from crankcase chamber 68 to crankcase chamber 34 at the samerate as the internal leakage between the suction chamber 66 and thecrankcase chamber 68. On a rise in high-stage suction pressure inchamber 66, the internal leakage will increase and thepressure-regulating valve will close until the pressure in the crankcasechamber 68 builds up to within one pound of the pressure in the suctionchamber 66 at which point the pressure-regulating valve 72 will againopen. On a drop in high-stage suction pressure, the pressure-regulatingvalve will open wide to immediately reduce the pressure in crankcasechamber 68 to one pound below the pressure in suction chamber 66.

By maintaining the pressure in the crankcase chamber 68 one pound belowthe pressure in suction chamber 66, the possibility of any oil vaporaccumulatf ing in the suction chamber 66 from the crankcase chamber 68is substantially prevented. In the event any oil vapor in the dischargerefrigerant from the lowstage discharge chamber 30 accumulates in thehighstage suction chamber 66, the accumulated oil will be allowed toreturn to the crankcase chamber 68 by the automatic oil drain assembly70. The high-state compressor 12, therefore, acts as a final filter inthe event of any oil vapor passing from the low-stage compressor 10 tothe high-stage compressor 12.

The high-stage crankcase chamber 64 is connected to the low-stagecrankcase chamber 34 to prevent any loss of oil from the system. In thisregard, the oil vapor within the crankcase chamber 68 will pass to thecrankcase chamber 34. It should be apparent that with this arrangementoil will accumulate in chamber 34 and the oil level in chamber 68 willcreep below normal. This can be compensated for by connecting an oilpump to respond to the oil level in chamber 34 and to pump oil fromchamber 34 to chamber 68.

RESUME The present invention provides for an oil-free operation of atwo-stage drywall compressor for a refrigeration system. This isaccomplished by holding the pressure in the high-stage suction chamberhigher than the pressure in the high-stage crankcase chamber. Thispressure differential is controlled by a pressure-regulat- 1 ing valvewhich is connected to respond to the suction chamber pressure and thecrankcase chamber pressure. Internal gas pressure leakage in thehigh-stage compressor will always be from the suction chamber to thecrankcase chamber.

I claim:

1. A refrigeration system comprising,

a condenser,

a receiver,

and an evaporator,

a low-stage drywall compressor and a high-stage drywall compressoroperatively connected to said condenser, receiver, evaporator and toeach other, each compressor including a discharge chamber, a suctionchamber and a crankcase chamber,

first means for draining oil from said low-stage suction chamber to saidlow-stage crankcase chamber,

second means for automatically draining oil from said high-stage suctionchamber to said high-stage crankcase chamber,

and means for maintaining a predetermined pressure differential betweensaid high-stage suction chamber and said high-stage crankcase chamber.

2. The system according to claim 1 wherein said maintaining meansincludes a pressure-responsive valve connected to vent said high-stagecrankcase chamber and connected to respond to the discharge pressure ofsaid low-stage discharge chamber.

3. The system according to claim 2 wherein said valve is set to maintaina one-pound pressure differential between the high-stage suction chamberand the high-stage crankcase chamber.

4. The system according to claim 1 wherein each of said oil-drainingmeans includes a reservoir operatively connected to allow oil to drainfrom the corresponding suction chamber to the reservoir and from thereservoir to the corresponding crankcase chamber and including meansresponsive to the level of oil in the reservoir for selectivelyconnecting said reservoir in gas-pressure equalizing relation to one ofthe corresponding suction chambers or discharge chambers. v

5. The system according to claim 1 including a first gas pressureconduit connected between said highstage crankcase chamber and saidlow-stage crankcase chamber, and a second gas pressure conduit connectedbetween said low-stage discharge chamber and said high-stage suctionchamber, said maintaining means in- 0 eluding a pressure-responsiveregulating valve interposed in said first gas pressure conduit andconnected to said second gas pressure conduit.

6. The system according to claim 5 wherein said valve is set to maintainthe pressure in said high-stage suction chamber higher than the pressurein said highstage crankcase chamber.

A refrigeration system having a condenser, a

receiver, and an evaporator operatively connected to a first stagedrywall compressor including a first stage suction chamber, a firststage discharge chamber and a first stage crankcase chamber, and asecond stage drywall compressor including a second stage suctionchamber, a second stage discharge chamber, and a second stage crankcasechamber, a gas refrigerant conduit connecting said first stage dischargechamber in gas pressure relation to said second stage suction chamber, agas pressure conduit connecting said second stage crankcase chamber ingas pressure relation to said low-stage crankcase chamber, and meansinterposed in said gas pressure conduit for controlling the pressure insaid second stage crankcase chamber.

8. The system according to claim 7 wherein said controlling means inconnected to said gas refrigerant conduit to maintain a predeterminedpressure differential between said second-stage suction chamber and saidsecond-stage crankcase chamber.

9. The system according to claim 7 including means for equalizingpressure between said first-stage suction chamber and said first-stagecrankcase chamber, first means operatively connected to said first-stagesuction chamber and said first-stage discharge chamber for draining oilfrom said first-stage suction chamber and discharging oil under pressureinto said first-stage crankcase chamber, and second means operativelyconnected to said second-stage discharge chamber and said second stagesuction chamber for automatically draining oil from said second-stagesuction chamber and discharging oil into said second stage crankcasechamber.

* fil

1. A refrigeration system comprising, a condenser, a receiver, and anevaporator, a low-stage drywall compressor and a high-stage drywallcompressor operatively connected to said condenser, receiver, evaporatorand to each other, each compressor including a discharge chamber, asuction chamber and a crankcase chamber, first means for draining oilfrom said low-stage suction chamber to said low-stage crankcase chamber,second means for automatically draining oil from said high-stage suctionchamber to said high-stage crankcase chamber, and means for maintaininga predetermined pressure differential between said high-stage sUctionchamber and said high-stage crankcase chamber.
 1. A refrigeration systemcomprising, a condenser, a receiver, and an evaporator, a low-stagedrywall compressor and a high-stage drywall compressor operativelyconnected to said condenser, receiver, evaporator and to each other,each compressor including a discharge chamber, a suction chamber and acrankcase chamber, first means for draining oil from said low-stagesuction chamber to said low-stage crankcase chamber, second means forautomatically draining oil from said high-stage suction chamber to saidhigh-stage crankcase chamber, and means for maintaining a predeterminedpressure differential between said high-stage sUction chamber and saidhigh-stage crankcase chamber.
 2. The system according to claim 1 whereinsaid maintaining means includes a pressure-responsive valve connected tovent said high-stage crankcase chamber and connected to respond to thedischarge pressure of said low-stage discharge chamber.
 3. The systemaccording to claim 2 wherein said valve is set to maintain a one-poundpressure differential between the high-stage suction chamber and thehigh-stage crankcase chamber.
 4. The system according to claim 1 whereineach of said oil-draining means includes a reservoir operativelyconnected to allow oil to drain from the corresponding suction chamberto the reservoir and from the reservoir to the corresponding crankcasechamber and including means responsive to the level of oil in thereservoir for selectively connecting said reservoir in gas-pressureequalizing relation to one of the corresponding suction chambers ordischarge chambers.
 5. The system according to claim 1 including a firstgas pressure conduit connected between said high-stage crankcase chamberand said low-stage crankcase chamber, and a second gas pressure conduitconnected between said low-stage discharge chamber and said high-stagesuction chamber, said maintaining means including a pressure-responsiveregulating valve interposed in said first gas pressure conduit andconnected to said second gas pressure conduit.
 6. The system accordingto claim 5 wherein said valve is set to maintain the pressure in saidhigh-stage suction chamber higher than the pressure in said high-stagecrankcase chamber.
 7. A refrigeration system having a condenser, areceiver, and an evaporator operatively connected to a first stagedrywall compressor including a first stage suction chamber, a firststage discharge chamber and a first stage crankcase chamber, and asecond stage drywall compressor including a second stage suctionchamber, a second stage discharge chamber, and a second stage crankcasechamber, a gas refrigerant conduit connecting said first stage dischargechamber in gas pressure relation to said second stage suction chamber, agas pressure conduit connecting said second stage crankcase chamber ingas pressure relation to said low-stage crankcase chamber, and meansinterposed in said gas pressure conduit for controlling the pressure insaid second stage crankcase chamber.
 8. The system according to claim 7wherein said controlling means in connected to said gas refrigerantconduit to maintain a predetermined pressure differential between saidsecond-stage suction chamber and said second-stage crankcase chamber.